The invention relates to a method for cleaning a first filter and a second filter of a suction device for cleaning purposes, which comprises a dirt collection container with a suction inlet, wherein the dirt collection container is subjected to negative pressure via the first filter and the second filter and a first suction line and a second suction line, respectively, following the first filter and the second filter, wherein a first closing valve and a second closing valve close a first external air inlet and a second external air inlet, respectively, into the first suction line and the second suction line, respectively, and wherein to clean the first filter and the second filter, the first closing valve and the second closing valve, respectively, are opened, in order to subject the first filter and the second filter, respectively, to external air on the clean space side.
The invention also relates to a suction device for cleaning purposes with a dirt collection container, which comprises a suction inlet, the suction device comprising at a first suction outlet a first filter and at a second suction outlet a second filter, which are followed by a first suction line and a second suction line, respectively, via which the dirt collection container can be subjected to negative pressure, and the suction device comprising a first external air inlet and a second external air inlet, via which external air can flow into the first suction line and into the second suction line, respectively, in order to subject the first filter and the second filter, respectively, to external air on the clean space side, and which are closable by a first closing valve and a second closing valve, respectively.
Such a suction device, with which the above method may be performed, is described in US 2005/0011036 A1 in the form of a vacuum cleaner. The vacuum cleaner comprises two or more filters, with each of which there are associated a suction line and a closing valve connected into the latter for selective admission of external air via external air inlets. The suction lines open into one another and can be subjected to negative pressure by a suction unit. During normal suction operation, the external air inlets are closed by the closing valves, and the dirt collection container is subjected to negative pressure via all of the suction lines. This allows suction material such as, for example, dirt or liquids to be sucked in at the free end of a suction hose connectable to the suction inlet and deposited in the dirt collection container. During continuous suction operation, particles of dirt may settle on the filters and clog these, which results in a rise in the pressure in the dirt collection container and, consequently, in reduced suction power of the vacuum cleaner.
To clean one of the filters, US 2005/0011036 A1 proposes opening the external air inlet of the associated suction line by means of the associated closing valve, whereas the external air inlets at the remaining suction lines remain closed by the further closing valves. External air, for example, at atmospheric pressure, can flow through the open external air inlet into the suction line and act upon the filter to be cleaned on the clean space side. Owing to the difference between the pressure of the external air and the pressure of the air in the dirt collection container, the filter to be cleaned experiences a pressure surge, as a result of which particles of dirt are dislodged from the filter and deposited in the dirt collection container. The external air can continue to flow through the filter to be cleaned and enter the dirt collection container, from which it can be sucked off via the remaining filters and the suction lines associated with these by means of the suction unit. After that the closing valve can be closed and, if required, a further closing valve opened, in order to clean a further filter.
In the method described in US 2005/0011036 A1, it has proven disadvantageous that both the external air that has entered the dirt collection container via the open external air inlet and the filter to be cleaned and the suction air drawn in through the suction hose have to be sucked off by the suction unit. When external air flows into the dirt collection container, this brings about an uncontrollable rise in pressure in it. In practice, this may result in the negative pressure provided by the vacuum cleaner at the free end of the suction hose no longer being adequate to suck in suction material.
This problem occurs, in particular, with suction hoses having a relatively large diameter, in particular, larger than 40 mm and, for example, 60 mm. Such suction hoses are used, for example, when vacuuming machining tools, in particular, drilling, milling or sawing units.
Particularly large suction cross sections of the suction inlet are present in suction devices in the form of vacuum sweepers, in which the uncontrollable rise in pressure in the dirt collection container has also proven disadvantageous.
The object of the present invention is to develop a generic method and a generic suction device so as to obtain a better suction result.